Four people have been killed and at least 50 hurt in an explosion in the Turkish capital, Ankara, officials say.

The cause was not immediately clear but the city's Mayor Melih Gokcek said police believed a bomb was to blame.

The blast occurred during evening rush hour at the entrance to a shopping centre in the busy district of Ulus.

The scene has been cordoned off and an investigation has begun. Unconfirmed reports suggest an explosive device may have been left at a nearby bus stop.

Recent attacks

Much of the front of one building was ripped off by the blast at the Anafartalar shopping centre.

TV footage showed several people lying seriously injured on the pavement surrounded by piles of concrete and glass. Other people, possibly passers-by, were hurt by flying glass.

Turkey has been hit by bombings in recent years. Some have been blamed on Kurds and others on Islamic militants.

In November 2003, more than 60 people were killed by a series of suicide bombings in Istanbul which the authorities linked to al-Qaeda.

Kurdish rebels carried out a spate of attacks on tourist sites in Turkey last year, killing more than a dozen people.

PHOTO CAPTION

TV footage of injured civilians being stretched in ambulances